Thread: Mit-a-mit

Not sure if you guys will be able to see this in the photo but the end of the upper portion of the shaft is tapered where the 30T gear will sit. The ratchet bracket goes behind and a small curved spacer in front on the step down. so other than the ball handle screwed on how does this all mechanically fit together?

Originally Posted by DSEL74

The small one is currently a press fit,

Originally Posted by DSEL74

Not sure if you guys will be able to see this in the photo but the end of the upper portion of the shaft is tapered where the 30T gear will sit.

Well thats a pity
Does the small gear* slide on past the taper? If so you're up for a new gear* or boring the gear* and making a tapered bush to fit.

Originally Posted by DSEL74

. so other than the ball handle screwed on how does this all mechanically fit together?

The ratchet bracket will be a sliding fit on the shaft and I assume the ball handle pushes the "tapered" gear* onto the shaft and holds it there. (there is no key?)

Stuart

I would suggest that the ratchet gear is taper bored and relies on the 3 ball handle to push it on (bit like a boat prop, although they also have a key) Once you work out the taper though it should not be hard to centre the wheel and using the cross slide bore the taper. Worst comes to worst and you have to bore the ratchet wheel (larger), insert a new piece of material and bore that.

Michael

It seems I'm a bit lucky fella, I hadn't the correct size reamer so I hadn't dobe the gear. So it just goes on a few mm. So instead of reaming I need to make it a taper..

Made a start on the cam shaft?? Don't laugh at me it's a Hacksaw and file job. No fancy mill here, not even a working shaper! Lol

Originally Posted by DSEL74

Made a start on the cam shaft... it's a Hacksaw and file job. No fancy mill here, not even a working shaper! Lol

Noting wrong with that if you haven't got means. It will get the job done.
The original piece was brass - plain bearings work better when there is a soft- hard combination - and you have steel-steel (so two the same hardness). That can still work but while you are making I would suggest putting a groove inside the hole and then running a grease nipple into it so that you can lubricate the running surfaces well. Otherwise if are not careful one day it could bind up.

Michael

Looks damn good to me....... I'd still be thinking about it.

Michael,

Do you think boring the conrod(?) oversize and fitting a ring made of 0.5mm brass be an improvement?

Stuart

Originally Posted by DSEL74

The large one needs to be 12.7 (½" actually) so I need to figure out which is the true ½" the hole or the shaft and which has the tolerance. The I will enlarge the hole to 1/32 undersize and ream it out also. I'm assuming I will have adjustable reamer of the correct size and useable.

It is possible you have some wear on the shaft, so sizing the gear to the 'as new' size may not produce what you expect. I find that if you can ream a hole to 0.001" to 0.002" over the size of your shaft, that is a nice fit (under and it is harder get on, over and clearance can make it wobbly side to side). There does need to be space in there for grease or oil too. Those are the numbers I usually shoot for - others may have better ideas.
Adjustable reamers are a sneaking up thing. 1/32 will be too much to take out in one pass. Numbers I've seen for fixed reamers suggest allowing 5 thou under the final size, so if you figure you can only take out 5 thou at a time, 1/32 could take a while. Chatter can be a problem so use a pilot or a centre in the back of the reamer while the wheel is mounted in the lathe for boring (similar to the way you hold a tap straight) - don't try it under power though. Measuring an adjustable reamer accurately is tricky and I find they will settle slightly once cutting. Start under and measure the hole you produce rather than the reamer. Creep up on the hole (maybe an 1/8 of a turn on the nuts - you'll get the hang of it) until you get the size right. If you haven't got a good way of measuring the hole diameter accurately, use an external mic to measure the shaft and then make up a dummy shaft the same size to use as a gauge. Safer than using using calipers or telescopic gauges if you are not practiced with them. Put a chamfer on your gauge and take off any burrs you might have as if you don't Murphy's law says that you will adjust until the burr clears and then have an oversized hole.

Michael

Originally Posted by Stustoys

Do you think boring the conrod(?) oversize and fitting a ring made of 0.5mm brass be an improvement?

My first preference would be solid brass. A ring 0.5mm thick may work in theory but I would be concerned that at that thickness it could easily get knocked, folded or dislodged. Securing it may be difficult too. The eccentric is around 1 1/4" from memory so if there was room to shrink in a ring with say a 3mm wall that may be better than a thinner section. Steel should work if well lubricated and it may be a good stop gap rather than spending on brass to find that the shape is wrong or there is some other problem. It can always be remade later once the shape is proven.

I think the live steam guys call these things eccentrics or straps(?).

Michael

The eccentric is on the shaft and the eccentric strap goes around it.
Yee ha, something I know.

Phil

The eccentric strap on the original had a bush on the ratchet end so I assumed that was a bronze bush. I guess that it could have been a steel bush in a brass strap. I will have to go back to the photos. The wall of the loop is only ~4mm so not much room to sleeve it.

Looking at post 78, it looks brassy to me but that could be a trick of the light. The bush looks like steel - which would be good because you will tighten up on that and pivot on the outside surface.

Michael

PS - Well done Phil. As I wrote that I was thinking "I'm sure that Phil would know this"

On the left is the is eccentric gear and the eccentric strap. On the right is all the bits that hold the 30T gear on the worm. Note the spacer.

MitaMit B133 37.jpg
Looks like it could be brass with a steel bush. The ratchet arm probably was a brass casting also. So I'll finish the steel one off and make up a brass eccentric strap at a later date. Once it all works and is proven.
MitaMit B133 43.jpg




*** Had confirmation it was chrome plated bras. That explains the patchy silver - gold color..

Originally Posted by Michael G

The eccentric is around 1 1/4" from memory

The scale of this thing keeps throwing me off.
I was thinking getting a piece of brass "that big" would be pricey.. turns out that big isnt that big

I'll be in touch next week sometime Dale

Stuart

Originally Posted by Stustoys

The scale of this thing keeps throwing me off.
I was thinking getting a piece of brass "that big" would be pricey.. turns out that big isnt that big

I'll be in touch next week sometime Dale

Stuart

The strap is 9mm thick and under 90mm long x 50mm wide.